In computer networking, there are many reasons why a client system may achieve a connection to a remote host system, but obtain poor performance with respect to that connection. Some of the metrics commonly used to indicate performance are packet loss (intermittent failure for packets of data to arrive), latency (round-trip response time, hence responsiveness) and throughput (overall rate of data transmission).
Numerous known solutions in computer networking technology conceal temporary problems by means of abstraction in software, creating an artificial scale separation. Internet protocol (IP) networking and numerous related inventions reduce inherent risks, principally by allowing a connection to be re-routed and re-established when seriously disturbed or broken, provided that there are alternative paths and that any congestion is temporary.
These normal tools to improve connection stability and performance under cover of abstraction, including timeouts built into the transmission control protocol (TCP), are optimized for the range of stabilities found in wired solutions. They are correspondingly maladapted to mobile, wireless communication. They achieve little in the simple case of a client being connected to its host through a single network node, such that all traffic must, in practice, be routed over a fixed path through that part of its journey, and any response must take the same path back. The slowest individual segment of such a path has the largest impact on overall performance.
Wireless wide-area network (WWAN) communication technologies, such as HSPA and LTE, often produce poor performance in spite of the normal tools. These technologies provide a wireless link between a client, such as a cell phone, and a base station. The base station, commonly called a cell tower, has a wired connection to other parts of the network operator's infrastructure. Because WWAN technologies require a wireless step in networking, the overarching network connection becomes susceptible to degradation from a variety of physical phenomena largely or wholly absent in wired communication. One example is the occurrence of Rayleigh fading as a result of movement in the radiophysical environment, such as when a cell phone (client) on a moving vehicle communicates with one or more base stations along the vehicle's route.
Many of the reasons why a wireless network connection may be poor are difficult or impossible for a single client to diagnose. For instance, there may be so many competing WWAN clients that each one is assigned a narrow channel of the radio spectrum licensed for the technology, or get bumped off to more distant base stations, producing a weaker signal. Only some modems permit a user to identify such congestion directly. As another example, the backhaul wire between the base station and the network operator's connection to core Internet infrastructure may be inadequate for the volume of traffic, forcing the network operator to apply some method of triage unknown to the client.
In particular, problems are present in moving vehicles, and in particular when multiple users/clients travel together on larger vehicles, such as buses, trains and the like. At the same time, there is today an increasing demand from passengers to be able to communicate through mobile phones and other handheld terminals when travelling on e.g. trains, and also to be able to get access to the Internet with laptops, PDAs etc. Further, with the new smartphones, and the way these are used, with e.g. continuously operating applications, many phones are active at all times, meaning that many handovers are required when the train moves. Even though this problem is common for all moving vehicles, it is especially pronounced for vehicles moving at high speed, such as trains.
EP 1 175 757 by the same applicant describes a method whereby many of these weaknesses resulting from wireless communication may be overcome through the concurrent use of multiple links, including both wired and wireless technologies. Optimizations for performance and cost are mentioned. However, the aforementioned solution is often insufficient to obtain an optimal transmission performance. Trains and other moving vehicles often pass through areas with bad radio coverage, and present solutions are often unable to handle the required traffic.
There is therefore a need for an improved wireless communication system for moving vehicles, which provides better capacity utilization. Even though the above discussion is focused on trains, similar situations and problems are encountered in many other types of moving vehicles, and in particular moving passenger vehicles, such as buses, ships and airplanes.